The present invention relates to resins containing polymer chains that bear functional chemical groups and to the products thereof. In particular, linear polysulfone and polyethersulfone polymers or oligomers are synthesized with thermally and/or chemically active functional groups at the end of the chains. These groups, at a subsequent time, are activated to yield chemically cross-linked polysulfones and polyethersulfones.
For many applications, it is desirable to employ thermoplastic resins. Although such resins and their applications are well known, the use of thermoplastic resin reinforced by fiber is a relatively new art. The advantages of this art are significant. Fiber toughens and stiffens the resin to produce high performance products. At the same time, processing is facilitated because the fiber reinforced resin maintains its thermoplastic character. For example, a sheet of fiber reinforced resin can be heated and then stamped into desired shapes of appropriate metal dies. Furthermore, shapes can be altered as desired.
On the other hand, although thermosetting resins are generally used in fabricating fiber reinforced composites, fashioning shapes by thermoforming is not readily possible when thermosetting resins are used. Such products must be fashioned within the constraints of dies. Once formed, they cannot be reshaped; thus, errors are not correctable and shape adjustments are not possible. A sheet of fiber reinforced thermosetting resin, fully cured, cannot be thermoformed into the desired shapes. Although thermoplastic resins exhibit processing advantages over themosetting resins, they exhibit, in general, a serious deficiency in properties, i.e., a tendency to be solvated and thus weakened by organic solvents. This deficiency has severely limited the application of fiber reinforced thermoplastic resin composites. For example, circuit boards, boards prepared from fiber reinforced thermoplastic resin, cannot be cleaned by solvents commonly used in the manufacture of circuit boards. In the use of thermoplastic composites for aircraft, a signficant amount of product loss is incurred when aircraft hydraulic fluids and cleaning fluids come into contact with composites.